Catalytic precipitation of nickel, cobalt and zinc sulfides from dilute acid solutions



United States Patent CATALYTIC PRECIPITATION OF NICKEL, COBALT fiD ZINCSULFIDES FROM DILUTE ACID SO- TIONS Tuhin Kumar Roy, Calcutta, India,assigner to Chemical Construction Corporation, New York, N. Y., acorporation of Delaware No Drawing. Application June 21, 1954, SerialNo. 438,315

7 Claims. (Cl. 75-108) This invention is concerned with thehydrometallurgical production of metallic cobalt and nickel,particularly from non-sulfide ores. Still more particularly, the-presentinvention is concerned with a method of concentrating the nickel andcobalt values of non-sulfide ores while separating them from iron,aluminum, and other nonferrous metals by selective precipitation fromacidic leach liquors using hydrogen sulfide and a suitable catalyst.

In my copending application with F. A. Schaufelberger for United StatesLetters Patent, Serial No. 438,316, filed June 21, 1954, entitledPrecipitation of Non-Ferrous Metal Sulfides from Acidic Solutions, ithas been shown that aqueous acidic leach liquors can be treated toprecipitate cobalt and nickel values as their sulfides. This isaccomplished by adjusting the acid content of the liquor followed bytreatment at elevated temperatures with a nucleating agent under arelatively high overpressure of hydrogen sulfide.

It is not always possible or desirable to carry out-the process at theseconditions. It is, therefore, the purpose ofthe present invention todevise a process which is capable of selectively precipitating dissolvednon-ferrous metal values from an acidic liquor at lower temperature andat lower contents of free acid. Such a process, to be consideredsuccessful, should recover at least 98% of the metal or metals ofinterest. Preferably the precipitate should not assay more than about34% contaminant metals such as iron, aluminum, manganese, magnesium andthe like which usually dissolve concomitantly with cobalt and nickelduring leaching. Such a process also should be capable of precipitatingsubstantially all of any zinc present in the leach liquor. Precipitationshould be completely obtainable in a period of two hours and preferablyless than one hour.

' In the previously identified copending application, it was pointed outthat using a high reaction temperature, above 90 C. and preferably fromabout 100 C. to about 150 C. or higher and a relatively highoverpressure of H28 was considered necessary. This was based on thelower temperature and acidity by the use of suitable catalyst materialby treatment started at a temperature of from about 60 65 C. in thepresence of a small quantity of any finely-divided solid catalystmaterial. If so desired,

I the nucleating agent of the above-identified case may be used. Typicalexamples of the latter include graphite, kieselguhr or infusorial earthand the like, talc or finely ground sulfides or oxides of one or more ofthe metals being precipitated. l

As cobalt and nickel source material for the-present invention, anyliquor containing'dissolved salts of the desired metals can be used. Ofprimary interest are such liquors obtained by leaching, usually acidic,of suchores as are variously referred to as lateritic, oxidized,siliceous, weathered-silicate or non-sulfide ores. "For thepurpose ofthis discussion, they will be referred to as non-sulfide ores becauseWhile otherwise varied, they are characterized by an absence of sulfur.They may be leached by any desired method which inherently .or bysubsequent adjustment produces an acidic solution. I 1

Since sulfuric is the acid most commonly used inleaching on ores of thistype, it too will be taken as illustrative. After leaching, anillustrativepregnant leach liquor might be found to contain thefollowing dissolved ,content in grams per liter: I a a N1 3-. '-12.0 CO"0.2-0.7 Fe++ 0.5-2.0 Al 2.0 s.0 Mn 1.0-5.0 Mg 0.5-2.0 H2304 15-30Although these values are not intended to be limiting on the process,discussion of such a solution Willbe taken as typical. U I

The process of the present invention is, of course, equally applicableto leach liquors obtained by the leaching of sulfide ores. However, ithas lesspractical importance in that field because leaching methods areknown fonmetal sulfide ores which provide, leach liquors that do: notrequire the treatment of ,thepresent invention. Whatever the source, theliquor can be advantageously treated by the process of the presentinvention, when it is desired to purify and concentratethe cobalt andnickel values into the smallest possible bulk for further treatment.

At the completion of leaching, which as noted may have been carried outin any desired manner, the final content of dissolved free acid may beand usually is too highlfor the purposes of the present invention. Thefirst positive step, therefore, is to adjust the acid content of the,liquoras may be required. It is undesirable toexceedan acid content ofabout 34% at any time, even at the end of the reaction. At this aciditythe reaction rate becomes too slow. Some control must be exercised toinsure against this occurrence which would prevent completeprecipitation in the time available.

In this respect, the original solute content-of the liquor is ofimportant consideration in sOmecasesL Consumption of hydrogen sulfideduring reaction causes .the acidic content of the liquor to increase asthe metal sulfide precipitates. If the original metal salt content issufliciently high, the resultant increase in acid concomitant withprecipitation of the sulfide mayrcsult inexceeding the upper limitingfactor. v I p v f Ordinarily, this necessity for controlling theterminal acid condition will not be too serious 2. problem. Perhaps thesimplest approach is to adjust the initial vpHto some value which willprevent the increase in acidity during reaction carryingthe resultantacid content to .too high a level. In general, this will be to aninitialflacid content not less than about pH- 3.5. 'At'higher' pHvalues, precipitation is no longer sufficientlyselect'ive and otherprecipitates may be formed. Aluminum canb'e particularly troublesome.With oresfrequently encountered in the field, the aluminum contentwhichdissolve'sj 'during leaching is fairly high. At a pH'of about' 3. 5it is readily possible for aluminum hydroxide to exceed the solubilityproduct and precipitate.

In general, therefore, it'is undesirable to go above about pH 3.0 in theneutralizing step. Particularly is this true when operating a continuousflow scheme. When the process is operated on a batch basis it may becarried out at any pH at which hydroxides do not form. If the solutionis treated on a batch basis it may be possible in some cases to go to aninitial pH as high as or 6. When the process approaches neutrality orbasic conditions, particularly where ammonia in sufiicient amounts toform ammoniacal complexes is used, the resultant slurry is particularlyhard to filter and handle.

On the other hand, it is undesirable to have the initial pH much lessthan about 1.0. In general, the lower the acidity the faster thereaction rate and for an initial pH of less than about 1.0 the overallrate is apt to be slow. In general, then, the initial acid contentadjustment, if necessary, will be to a pH of from about 1.0 to about3.0. A preferred practice for the illustrative solutions would be fromabout 2.0 to about 2.5. Usually this will be adequate as an overallcontrol. In the few cases where it is not, because of high metalcontent, the use of hydrogen sulfide may be supplemented by the use ofsome acid neutralizing agent such as ammonia or ammonium or sodiumhydroxide. It may also be supplemented or replaced in whole or in partby a different source of sulfide ions. This may include using suchreactants as sodium sulfide, ammonium sulfide or their chemicalequivalents which will form soluble salts rather than free acid.

Generally, but not necessarily, neutralization will be carried outcommercially with limestone or its equivalent. Since this introducesinsolubles it will preferably be done before separation of the leachliquor from its accompanying solids. In some cases, as where noprecipitate forms during neutralization or no insoluble is introduced,or where it is desirable to isolate any precipitate formed,neutralization may be carried out after decanting the leach liquor fromthe residual solids. In any case, leach liquor is separaed fromaccompanying solids, the latter usually being washed and clarifiedliquor with or without washings, is sent to subsequent treatment.

Of primary importance in the present process, is the utilization of acatalyst. The selection of a catalyst will depend to some extent uponthe nature of the solution. Therefore, for this purpose in the presentinvention the same illustrative liquors obtained by sulfuric acidleaching of non-sulfide ores which are discussed above will beconsidered typical. A list of satisfactory catalysts for such a solutionwould include powdered metallic iron, nickel and mixtures of nickel andcobalt. Use of powdered iron as the catalyst does not present acombination problem. Since the sulfides product in any case is to beredissolved for further treatment, the small amount of iron added ascatalyst is of no importance and can be easily eliminated in thattreatment. Where speed of reaction is primarily important, freshlyreduced iron powder, as the fastest acting catalyst, is perhaps to bepreferred. However, it is less selective also and tends to produce inthe sulfide precipitate a higher content of iron and aluminum compoundsthan when nickel and/or cobalt metal is used. Hydrogen gas can be used.But from a handling point of view, a gas is not as simple as the use ofsolids. In amount, the catalytic metal added for the purpose willusually range from about 0.03 to about 5 grams per liter. More can beused.

In addition to the added catalyst, it is highly desirable to add someseeding or nucleating agent. Probably the most useful material for thispurpose is some of the product nickel sulfide or cobalt sulfide ormixture thereof which was produced in a previous run. This use of suchadded material may and usually does increase the rate of reaction tosome extent. This is probably due to the presence of some catalystmaterial in diluted form. Of

more practical importance is the fact that it reduces sulfidesdeposition on the walls of the pressure vessel in which the reaction iscarried out. The more finely divided the recycled sulfides, the moreeffective. They should be ambient temperatures, reaction is very slow.When the temperature reaches about 6065 C., the reaction rate becomeshigh enough for practical development. From 65 to about C. the reactionrate is effective. However, increasing the temperature above about 90 C.does not cause the reaction rate to increase noticeably within thepreferred range of acidity. Therefore, in most operations, thetemperature at which reaction is started should be somewhere from about60 to about 90 C. The reaction is exothermic to a considerable extentand once reaction has been started it is not at all difficult tomaintain this temperature range. Thorough agitation is highly desirable.

Reverting to consideration of the catalyst material used, it should benoted that size is of more importance, generally, than the weight ofcatalyst material which is used: Therefore, it may be considered thatthe higher the degree. of subdivision, the more active is the catalyst.In using a solid catalyst, in particular, it should be fed to thesolution in the smallest practicably obtainable sizes. This not onlyincreases the reaction rate but aids in preventing the objectionabledeposition of sulfides on the wallof the vessel. It is also of interestto note that, unlike most cases, it is desirable that the particles havesmooth surfaces, smooth, round particles being more effective thanrough, irregular ones.

It is an interesting feature of the present invention that it is notaffected adversely by sensitivity to the feed ratio of nickel to cobalt.In general, the process may be operated at any Ni:Co feed ratio rangingfrom 10:1, or more, in either direction.

The active reagent in the present process is hydrogen sulfide gas. It isobviously necessary that it be furnished in adequate quantities toproduce in solution the necessary sulfide ion concentration. Other thanthis, there is little effect from varying the rate of feeding the gas.According to the present invention, it has been found that this sulfideion concentration can be maintained by keeping a hydrogen sulfideoverpressure on the solution in a closed vessel. The hydrogen sulfideshould be bubbled in through the liquid below the surface. Successfulresults are obtained with pressures of about ten pounds per square inchgauge or more. H25 pressures up to about p. s. i. g. are readilyobtainable. Pressures above this point probably have no reallybeneficial effect and are not necessary except at high acidity outsidethe preferred range.

' In some cases, it may be questioned whether or not it is desirable torecycle the precipitate in building up the nickelzcobalt content of thesulfide precipitate. Where this is done, the recycle solid probably actsas noted above as an extender containing some catalyst metal. Generally,it will be found to have less active surface and excessive recycling mayresult in more plating on the walls than is desirable. In continuousoperation, however, to provide for uniformity of operation, it may bedesirable to recycle some of the product. Usually, if recycling for thispurpose is done, it will amount to some 50 to 200% of the circulatingload. In batch operation it is doubtful whether more than the smallamount desired to provide seeding surfaces for the sulfides are neededor will be recycled.

With this discussion in mind, the principal points of the process may besummarized as follows: adjusting the leach liquor, before or afterremoval of the undissolved tailings, to a pH of from about 1.5 to about3.0 and separation of resultant liquor from solids, the latter beingwashed and the washings either added to the liquor or recycled toleaching; placing clarified leached liquor in a suitable pressurevessel; adding thereto a small amount of catalytic iron, cobalt and/ornickel metal powder; subjecting the resultant mixture, with or without arecycled amount of ground, previously precipitated sulfides to agitationunder a hydrogen sulfide overpressure of from about to 100 p. s. i. g.or more at an initial temperature of from about 60 C. up to about 90 C.and continuing the reaction until the dissolved content of nickel and/or cobalt is sulficiently lowered.

Subsequently the sulfide precipitate is de-watered and washed. If sodesired, the sulfide is collected by froth flotation or the like.Collected sulfides are then subjected to further processing in which thecobalt and/or nickel content thereof is recovered. These latter stepsare not part of the process of the instant invention.

It is a feature of the present process that any manganese, magnesium,calcium and chromium content of the solution, together withsubstantially all the dissolved iron and aluminum, remain in thesolution. Cobalt and the nickel are substantially completelyprecipitated therefrom. When zinc is present it will be precipitatedwith the cobalt and/or nickel but is easily separated in the subsequentproduction of metal. If so desired, the liquor can be subsequentlyprocessed to recover one or more of these metals. Such treatment formsno part of the present invention.

The process of the present invention will be illustrated by thefollowing examples which are intended as illustrative only and not byway of limitation. In these examples, the concentration of dissolvedmetals is calculated for the metal content only and is indicated ingrams per liter (g./l.). All parts are by weight unless otherwise noted.

EXAMPLE l A sample of Cuban lateritic ore is subjected to ahightemperature sulfuric acid leaching. Decanted leach liquor containsthe following dissolved metal content in grams per liter (g./l.):Ni-5.6, Co-0.46, Fe++-1.1, Al5.9, Mn3.2, Mg-l.1, and free H2SO415. A1500 ml. sample of the solution is placed in an open vessel, neutralizedto a pH of 1.5 with soda ash, heated to 65 C. and hydrogen sulfide gasbubbled therethrough for one hour. No precipitation of sulfides whateveris obtained.

EXAMPLE 2 Another one liter sample of the leach liquor of Example l isheated in an open vessel to an initial temperature of 65 C. and H28bubbled therethrough for one hour in the presence of five grams of finepowdered nickel metal (100-325 mesh). At the end of one hour, 42% of thenickel and 39% of the cobalt are precipitated as their sulfides.

EXAMPLE 3 Example 2 is repeated placing 1500 ml. of the solution in apressure vessel equipped for agitation and subjected to a p. s. i. g.overpressure of HzS and 2.5 gms. per liter of nickel powder obtained byhydrogen reduction of nickel diammine sulfate solution. At the end of aone hour reduction, a precipitate is obtained containing 67.8% Ni, 3.8%Co, 0.036% Al, 0.65% Fe, 28% sulfur and a trace of manganese. Thefiltrate contains only 0.04 g./l. of nickel and 0.01 g./l. of cobalt.

EXAMPLE 4 A sample of the residual tailing solids after the leachingstep of Example 1 is ground to minus 325 mesh and then reduced withhydrogen for two hours at 800 C. and resultant solid precipitate of fineiron powder particles (averaging from 5 to 20 microns diameter) iscollected.

A one and one-half liter sample of the solution of'Example 1 is adjustedto pH 1.5with soda ash; 1.7 grams of the reduced iron powder is added,the mixture heated to C. and reduced in a pressure vessel under ahydrogen sulfide over-pressure of 25 p. s. i. g. for 90 minutes withagitation by a propeller-type stirrer turned at 600 R. P. M. Bothprecipitate and filtrate are analyzed. Precipitation is 99% complete asto cobalt and nickel, the filtrate analyzing 0.049 g./l. nickel and0.0046 g./l. cobalt. The precipitate analyzes as follows: Ni53.25%,Fe4.62%,

I Al-0.65%, Mnless than 0.01%.

The preceding example shows the efiiciency of the iron powder inproducing complete precipitation in the desired degree in a short time.However, it will be noted that the solids produced contain a moderatelyhigh content of iron and aluminum. That a solid precipitate lower iniron can be obtained using cobalt and/or nickel'as'the additive is shownin the followingexamples.

EXAMPLE 5 A sulfide precipitate was prepared by repeating the procedureof Example 3. Collected precipitate was roasted in air for one hour at600 C. The resultant calcine is reduced with hydrogen for two hours at400 0., yielding a finely divided cobalt-nickel mixed metal.

To 1.5 liters of the leach liquor of Example 1 is added sufficientsodium carbonate to produce a pH of about 1.5. To resultant solution isadded 1.7 grams of the reduced nickel-cobalt powder. The mixture isplaced in an autoclave under 25 p. s. i. g. overpressure of hydrogensulfide and at an initial temperature of 65 C. The mixture is treatedwith agitation for about two hours,- At the end of the period, 99.4% ofthe cobalt and 98.4% of the nickel is precipitated as arapidly-filtering sulfide residue. Analysis of the residue is asfollows: NiI-57.9%, Co-- 4.7%, Fe--1.2%, Al0.36%, Mn-0.001%.

EXAMPLE 6 In order to show the effect of varying the initial reductiontemperature, a series of sample of an aqueous sulfuric acid leach liquorcontaining 5.1 grams per liter of nickel (as sulfate) are reduced to aninitial pH of about 2.0, seeded with 0.5 g./l. of nickel seed powder(produced as in Example 5) and treated under about 25 p. s. i. 3. H23overpressure for varying periods of time. In one series, the intialreduction temperature is at ambient temperature; the second at 65 C. andthe third at 90C. At periodic intervals, the nickel content of thesolution is examined. Typical results are summarized in the followingTable I.

Table 1 [Residual dissolved Ni content (g./l.)]

Elapsed Time (Minutes) Initial Temp. C.)

5. o 4. 9 4. s 4. 7 4. "es 3. 8 2. 7 1. 4 0. 8 0. 5 0. 9 0. 3 0. l 0. 070. 05

EXAMPLE 7 In order to show the effect of the initial pH on nickelsulfide precipitation, a number of samples of an aqueous acidic leachliquor initially containing 5.8 g./l. nickel are seeded with 0.5 gramper liter of nickel powder (produced according to Example 3) and reducedunder 25 p. s. i. of hydrogen sulfide from an initial temperature of 65C. The residual liquor is examined at periodic inter vals to determineits residual nickel content. The initial pH is varied in succeedingseries. Typical results are summarized in the following table.

Table II {Residual dissolved Ni content (g./l.)]

Time (Minutes) Initial pH EXAMPLE 8 Table III [Residual dissolvedcontent (g.[l.)]

Time (Minutes) Initial pH EXAMPLE 9 In order to show the efiect on therate of nickel sulfide .precipitation of varying types of solidadditives, a number of samples of the leach liquor of Example 1 areneutralized with soda ash to an initial pH of about 2.0 and from aninitial temperature of 65 C. and under an HzS overpressure of 25 p. s.i. are reduced for varying lengths of time, the residual nickelconcentration of the solution being periodically examined. Illustrativeresults are shown in the following Table IV.

8 Table IV [Residual dissolved N 1 content (g./l.)l

Time (Minutes) Solid Added 10 2o 40 so so 4. 2 2. 9 1. 2+ 0.7+ 0. 5* 2.a 1.1 0. 31 0.11 0. 0a 1. 2 0. 5 0.15 0. 0s 0. as

I claim:

1. In the hydrometallurgical production of nickel and cobalt whereinnon-sulfide ores containing nickel, cobalt and iron are leached with anaqueous acid liquor and the cobalt and nickel content of the leachliquor is chemically precipitated, the improved method of concentratingand separating nickel and cobalt from iron and other non-ferrous metalimpurities which comprises the steps of: adding sufficientacid-neutralizing agent to adjust the free acid content of the liquor toa pH of from about 1.0 to about 3.0; adding to so-treated liquor fromabout 0.03 to about 10 grams per liter of a material selected from thegroup consisting of finely divided iron, nickel, cobalt and mixturesthereof; placing the mixture at a temperature of from about 60 C. toabout 90 C. under a positive overpressure of hydrogen sulfide gas andcontinuing treatment with agitation until sulfide precipitationsubstantially ceases.

2. A process according to claim 1 in which the liquor is clarified afterthe neutralization step.

3. A process according to claim 1 in which the initial neutralization isto a pH of from about 2 to about 2.5.

4. A process according to claim 1 in which the pew dered metal additiveis an iron powder of from about 5 to 50 microns average diameter.

5. A process according to claim 1 in which the solid additive is anickel metal powder.

6. A process according to claim 1 in which the solid additive is amixture of finely divided nickel and cobalt metal powders.

7. A process according to claim 1 in which the solid additive issupplemented by at least one material selected from the group consistingof finely-divided cobalt sulfide, nickel sulfide, and mixtures thereof.

References Cited in the file of this patent FOREIGN PATENTS 720,881Germany May 18, 1942

1. IN THE HYDROMETALLURGICAL PRODUCTION OF NICKEL AND COBALT WHEREINNON-SULFIDE ORES CONTAINING NICKEL, COBALT AND IRON ARE LEACHED WITH ANAQUEOUS ACID LIQUOR AND THE COBALT AND NICKEL CONTENT OF THE LEACHLIQUOR IS CHEMICALLY PERCIPITATED, THE IMPROVED METHOD OF CONCENTRATINGAND SEPARATING NICKEL AND COBALT FROM IRON AND OTHER NON-FERROUS METALIMPURITIES WHICH COMPRISES THE STEPS OF: ADDING SUFFICIENTACID-NETURALIZING AGENT TO ADJUST THE FREE ACID CONTENT OF THE LIQUOR TOA PH OF FROM ABOUT 1.0 TO ABOUT 3.0; ADDING TO SO-TREATED LIQUOR FROMABOUT 0.03 TO ABOUT 10 GRAMS PER LITER OF A MATERIAL SELECTED FROM THEGROUP CONSISTING OF FINELY DIVIDED IRON, NICKEL, COBALT AND MIXTURESTHEREOF; PLACING THE MIXTURE AT A TEMPERATURE OF FROM ABOUT 60*C. TOABOUT 90* C. UNDER A POSITIVE OVERPRESSURE OF HYDROGEN SULFIDE GAS ANDCONTINUING TREATMENT WITH AGITATION UNTIL SULFIDE PRECIPITATIONSUBSTANTILALY CEASES.